1. Field of the Invention
The present invention relates to an image processing apparatus capable of image processing such as gradation conversion utilizing image processing parameters based on characteristic values of an image taken for example with a radiation (such as X-ray).
2. Related Background Art
Certain luminescent substances, when subjected to radiation (X-ray, α-ray, β-ray, γ-ray, electron beam, ultra violet light etc.), accumulates a part of the energy of the radiation. Such luminescent substance, in a state of storing a part of the radiation energy, when irradiated with exciting light such as visible light, emits exhaustive light emission. The luminescent substance showing such property is called “photostimulable luminescent material”.
As the image pickup apparatus utilizing such photostimulable luminescent material, a radiation image information record/reproducing apparatus is disclosed for example in the Japanese Patent Application Laid-open Nos. 55-12429 and 56-11395.
In such radiation image information record/reproducing apparatus (hereinafter called “radiation photographing apparatus 1”), the radiation image information (for example X-ray image information) of an object such as a human body is once recorded on a sheet of the photostimulable luminescent material (photostimulable luminescent sheet). Then such photostimulable luminescent sheet is scanned with exciting light such as a laser beam to generate exhaustive luminescent light from the sheet and the generated exhaustive luminescent light is photoelectrically read to obtain an image signal. The obtained image signal is subjected to image processing such as gradation conversion, and thus processed image signal is outputted, in a visible form of the radiation image of the object, to a recording medium such as a photosensitive material or a display device such as CRT.
Also there is recently developed a photographic apparatus (hereinafter called “radiation photographing apparatus 2”) utilizing a semiconductor sensor to obtain the radiation image (X-ray image etc.) of the object in a similar manner as in the radiation photographing apparatus 1.
In comparison with the photographing apparatus (photoradiographic system) utilizing the conventional silver halide photographic technology, the above-mentioned radiation photographing apparatus 1 or 2 has a practical advantage capable of recording an image over an extremely wide radiation dose range.
More specifically, the radiation photographing apparatus 1 or 2 can acquire a radiation image not affected by the variation in the radiation dose, by converting the radiation, such as X-ray, of a very wide dynamic range after passing the object into an electrical signal by a sensor (photoelectric conversion means), and outputting the electrical signal after image processing to a recording medium such as a photographic sensitive material or a display device such as a CRT.
In such radiation photographic apparatus 1 or 2, it is required to automatically determine the parameters (image processing parameters) to be used for the image processing such as gradation conversion, in order to obtain the image of a density suitable for image observation (for example diagnostic observation by the doctor).
In general, the image processing parameters are classified into those dependent on the pattern of the photographed image (e.g., the photographing method, such as lateral chest photographing or thoracic vertebrae photographing; hereinafter also called “image pattern” or “photographing position”), and those not dependent on such image pattern. An example of a parameters dependent on the image pattern is the shift amount of the gamma curve upon graduation conversion, and an example of a parameters not dependent on the image pattern is the contrast of the gamma curve upon gradation conversion.
For example, it is desired, for the diagnosis of an image obtained by photographing a body portion from chest to lung (lung image), to execute the gradation conversion so as to obtain a gamma value of about 2.88. On the other hand, for an image obtained by lateral chest photographing of thoracic vertebrae (thoracic vertebrae image), it is desired for the diagnostic purpose to execute the gradation conversion so as to obtain a gamma value of about 4.
Therefore, in order to obtain a photographed image suitable for the diagnostic purpose, it is necessary, prior to the photographing or image processing, to acquire the information on the image pattern (photographing position) for example whether the intended image is a lung image or a thoracic vertebrae image.
Such information may be acquired by input by the user into the photographing apparatus (manual input method) or by automatic computer calculation in the photographing apparatus (photographing position judging method by a photographing position recognition program) without the manual input. For judging the photographing position of the medical image, there is known radiation image information reading methods as disclosed in the Japanese Patent Publications Nos. 06-077571 to 06-077579 and 06-093076.
However, the above-mentioned conventional photographing position judging methods are to judge the photographing position of the object image based on the characteristics of an accumulated histogram obtained from the images of different photographing positions or of accumulated profiles in the X and Y direction in the central portion of the image, and can only provide one-dimensional characteristic amounts for judging the photographing position since such accumulated histogram accumulated profile is obtained by converting a two-dimensional object image into one-dimensional information. Such characteristic amount is insufficient for judging the photographing position of the two-dimensional object image.
Also the judgment of the photographing position itself is rather simple (for example judging the front or side of the chest), and it has been impossible to finely judge the photographing position.
Also in the above-described photographing apparatus utilizing the photostimulable luminescent material, a cassette (IP) of the photostimulable luminescent material bearing the image has to be correlated with the object (patient etc.) by the assistance of an operator (radiologist or radiological technician (for example by a bar code reader), and the photographing position may be entered by the operator at such assisting operation. Such operation is very inefficient.
On the other hand, in a DR (direct radiology) system utilizing a semiconductor sensor, if the object information is once entered (patient registration) by the operator into the system, the image and the object are correlated without any intervention of the operator thereafter.
In the photographing apparatus of the DR system, it is strongly desired to execute the automatic judgment of the photographing position at a high precision, and to effectively utilize the result of such judgment.
However, as explained in the foregoing, the conventional judging methods for the photographing position are inadequate for judging the photographing position of the two-dimensional object image, and it has been not possible to realize the highly precise judgment of the photographing position since the judgment itself is rather simple.